WO2004087625A1

WO2004087625A1 - Process for producing isoprene

Info

Publication number: WO2004087625A1
Application number: PCT/JP2004/004038
Authority: WO
Inventors: Osamu Yamada; Manabu Kusano; Nobuo Takayanagi; Hideki Arimoto
Original assignee: Kuraray Co., Ltd.
Priority date: 2003-03-31
Filing date: 2004-03-24
Publication date: 2004-10-14
Also published as: EP1614671A1; JPWO2004087625A1; JP3917163B2; RU2320627C2; CN1768020B; CN1768020A; US7442844B2; EP1614671B1; EP1614671A4; RU2005133453A; US20070106104A1

Abstract

A process for producing isoprene which comprises continuously or intermittently feeding isobutylene and/or t-butanol, formaldehyde, and water into an acidic aqueous solution to react the reactants while distilling off a mixture comprising isoprene generated from the liquid reaction mixture, water, unreacted starting materials, and other low-boiling matter(s), wherein the reaction is conducted while regulating the concentration of high-boiling by-products which have generated and accumulated in the liquid reaction mixture to 0.5 to 40 wt.%.

Description

Method for producing isoprene

Technical field

The present invention relates to a method for producing isoprene. The isoprene obtained by the production method of the present invention can be effectively used as a basic chemical raw material for various chemical products and polymer raw materials.

Background art

As a method for producing isoprene, isobutylene and / or t-butanol (hereinafter, “isobutylene and / or t-butanol” can be abbreviated as “c ₄ ”) in a reactor containing an acidic aqueous solution. There is known a method in which formaldehyde and water are supplied continuously or intermittently, and the reaction is carried out while distilling the produced isoprene together with water and other low-boiling components out of the reaction system. (For example, see Japanese Patent Publication No. 59-70623)

In the production method described in JP-A-59-76023, a part of a mixture of C ₄ , formaldehyde, water and an acidic aqueous solution (hereinafter, abbreviated as “reaction mixture”) is used. was removed from the reactor, after it was heated together with at least a portion of the C _4, it is (e.g. is known a manufacturing method of introducing into the reactor again, JP 5 9 1 9 0 9 3 0 No.). Note that “water” may be understood to be included as an aqueous solution such as an acidic aqueous solution, and the “reaction mixture” may contain a product and a by-product of the reaction.

Further, in the production method described in Japanese Patent Application Laid-Open No. 59-70623, the isoprene, water, unreacted raw materials and other low-boiling components (hereinafter, referred to as distillate) which are distilled out of the reaction system as a gas. The “produced isoprene, water, unreacted raw materials and other low-boiling components” are abbreviated as “reaction distillate gas.”) The heat of water is recovered by mainly condensing water in Is used as a heat source for evaporating isobutylene and a heat source for recovering unreacted isobutylene by distillation from the organic layer obtained by condensing the reaction distillate gas and phase-separating it. Isoprene production method It is known (see, for example, Japanese Patent Publication No. 60-41838).

Furthermore, when separating high-boiling by-products accumulated in the reaction mixture, unreacted raw materials and isoprene are distilled off from the organic layer of the distillate from the reaction mixture or a part thereof. There is known a method for producing isoprene, which comprises adding a residue obtained by the above process or a part thereof and separating the residue into an organic layer containing the high-boiling by-product and an acidic aqueous solution (see, for example, 9-1 1 1 6 2 3 6).

However, the present inventors have studied the conventional methods for producing isoprene as described above, and have newly found that the following problems exist in these production methods.

That is, JP-A-59-70623, JP-A-59-19030, and JP-A-59-116326 disclose. Simply practicing the production method fluctuates the concentration of high-boiling by-products in the reaction mixture, resulting in unstable acid concentrations in the reaction mixture, which may lead to equipment corrosion and isoprene formation. There is a problem that the reaction performance deteriorates.

In particular, that extracts a part of the reaction mixture from the reactor, when heating the same time at least part of C _4, nor too low too high concentration of high boiling point byproducts in the reaction mixture, It was found that heat was not sufficiently transferred to the reaction mixture. If the heat is not sufficiently transferred, the temperature of the reaction mixture in the reactor gradually decreases, and the amount of water distilled out during the reaction tends to decrease. In order to keep the height of the reaction mixture level constant, the supply amount of formaldehyde aqueous solution must be reduced, and as a result, the production of isoprene per unit time tends to decrease.

On the other hand, in such circumstances, when the temperature of the reaction mixture in the reactor by excessive heating at least part of the reaction mixture and the C ₄ to withdrawn from the reactor you trying held constant, the production of isoprene The problem is that the efficiency of use of heat required for the process decreases, and the problem that pipes are easily clogged due to accumulation of high-boiling by-products in the pipes.

According to the production method described in Japanese Patent Publication No. 60-41838, the reaction distillate gas is Although the amount of heat it has can be effectively recovered and reused, it is not satisfactory as a supplement to the amount of heat required for the production of isoprene, and there is still room for improvement for industrial implementation.

An object of the present invention is to solve the above-mentioned problems and to provide a method for producing isoprene more efficiently than before.

Disclosure of the invention

The present invention achieves the above object by the following features.

(1) Isobutylene and / or t-butanol, formaldehyde and water are continuously or intermittently fed into an acidic aqueous solution, and isoprene, water, unreacted raw materials and other low boiling points are formed from the reaction mixture. A process for producing isoprene by distilling a mixture containing components out of the reaction system and reacting the mixture,

Performing the reaction while controlling the concentration of the high-boiling by-product generated and accumulated in the reaction mixture within a range of 0.5 to 40% by mass. Production method.

(2) A reactor containing the reaction mixture is provided with an outlet for the reaction mixture, a part of the reaction mixture is withdrawn from the outlet, and at least at least high-boiling by-products are removed from the reaction mixture. After separating and removing a part, the concentration of the high boiling by-product in the reaction mixture is controlled within the above range by introducing the mixture into the reactor again.

(3) The method for producing isoprene according to the above (2), wherein an outlet for the reaction mixture is provided at least at the bottom of the reactor.

(4) An outlet for the reaction mixture is provided on the side wall of the reactor, and the height of the outlet is adjusted to the height when the volume of the liquid when the reaction mixture is filled up to the height. The method for producing isoprene according to the above (2) or (3), wherein the height is set to be 1/2 or more of the total volume.

(5) A mixture containing the produced isoprene, water, unreacted raw materials and other low-boiling components is distilled out of the reaction system as a reaction distillate gas, and water is condensed from the reaction distillate gas. The process for producing isoprene according to any one of (1) to (4) above, wherein the obtained water is again introduced into the reactor to control the concentration of the high-boiling by-product in the reaction mixture within the above range. Method.

(6) The reactor is equipped with a stirring device that is configured so that the stirring blades rotate horizontally in the reaction mixture, and isoprene and / or t-butanol are piped to just below the stirring blades in the reactor. The concentration of the high-boiling by-product in the reaction mixture is controlled within the above range by supplying the mixture to the stirring blade from the inlet provided by extending the passage. (1) to (5) 3. The method for producing isoprene according to 1.).

(7) The reactor is provided with a stirring device that is configured so that the stirring blades rotate horizontally in the reaction mixture, and a part of the reaction mixture is withdrawn from the reactor, and this is removed with isobutylene and / or t-butyl acetate. After heating in a heat exchanger together with at least a part of the bottle, the mixture is introduced again into the reactor, and the heated reaction mixture is supplied to the stirring blade from an inlet provided in the reactor. The method for producing isoprene according to any one of the above (1) to (6), wherein the concentration of the high-boiling by-product in the reaction mixture is controlled within the above range.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram of manufacturing equipment for explaining the manufacturing method of the present invention.

FIG. 2 is a diagram schematically showing a configuration of equipment constructed to carry out the manufacturing method according to the present invention in the embodiment of the present invention. In the heat exchangers 2, 3, 5, 6, 7, and 11 shown in the figure, the connection inside the heat exchanger is schematically shown by solid lines and broken lines in order to clarify the input / output relationship of piping. However, these do not indicate the internal piping shape.

The meanings of the reference numerals in FIGS. 1 and 2 are shown below. A: Reaction mixture, Pl to P10: Pipeline, 1: Reactor, 2, 3, 5, 6, 7, 11, 12: Heat exchanger, 4: High-boiling by-product separation tank, 8, 9, 13: Distillation reservoir, 10, 14: Distillation tower.

BEST MODE FOR CARRYING OUT THE INVENTION

The method for producing isoprene of the present invention is schematically illustrated by the schematic diagram of the production facility shown in FIG. As shown, in an acidic aqueous solution in the reactor 1, the C ₄ from the pipe P 6, and continuously or intermittently supplying the formaldehyde and water from the pipe P 1, to produce et whether the reaction mixture A A method is used in which a mixture containing isoprene, water, unreacted raw materials, and other low-boiling components is reacted while distilling it out of the reaction system as a reaction distillate gas through a distillation line P2. The basic technology of this production method is the same as the conventionally known production technology of isoprene, and is described in JP-A-59-70623 and JP-A-59-190309. Reference may be made to Japanese Unexamined Patent Application Publication No. Sho 60-41838 and Japanese Unexamined Patent Application Publication No. 59-116 1636.

Here, an important feature of the present invention, which has not hitherto been, is that the concentration of the high-boiling by-product (not shown) generated and accumulated in the reaction mixture A is 0.5. The point is that the isoprene is produced while controlling the amount to be within the range of 40% by mass.

For example, Japanese Patent Application Laid-Open No. 59-70623 discloses removal of high-boiling by-products that accumulate during the reaction, and also describes the operation thereof. There is no description of the effect of the concentration on the reaction performance. On the other hand, in the present invention, it has been found that a new action and effect can be obtained by allowing a certain amount of the high-boiling by-product to be present in the reaction mixture, and the concentration is adjusted to 0.5 to 40% by mass. It is characterized in that the operation of removing high-boiling by-products is controlled within the range.

The high-boiling by-products whose concentration is controlled are usually widely dispersed in the liquid in the reactor, but may be unevenly distributed in the upper or lower part of the reaction mixture depending on the stirring efficiency. Although the components of the by-products cannot be specified, impurities such as high-boiling organic compounds such as products and by-product multimers in the isoprene production method of the present invention, reaction raw materials, and inorganic substances derived from the reaction apparatus are used. And the like.

By controlling the concentration of the high-boiling by-product in the reaction mixture within the range of 0.5 to 40% by mass, the high-boiling by-product preferably acts as a heat transfer medium. The heating efficiency of the reaction mixture using a heat exchanger or the like can be maintained at a preferable value, and troubles such as clogging of the pipeline by high-boiling by-products do not occur. This Thus, isoprene can be produced more efficiently than in the past.

The concentration of the high-boiling by-product in the reaction mixture is more preferably in the range of 1 to 30% by mass, and the heat exchange property and the suppression of trapping such as clogging of the pipe are highly enhanced. From the viewpoint of compatibility, it is particularly preferable that the content be in the range of 2 to 20% by mass. If the concentration of the high-boiling by-product in the reaction mixture is less than 0.5% by mass, the heating efficiency of the reaction mixture decreases, and in the following order, the temperature of the reaction mixture in the reactor decreases, and As a result, the amount of aqueous formaldehyde supplied to the reactor was reduced to maintain the level of the reaction mixture in the reactor at a constant level, and as a result, the amount of isoprene per unit time was reduced. Production volume decreases. In order to prevent the temperature of the reaction mixture in the reactor from lowering as described above, it is conceivable to overheat the reaction mixture in the heat exchanger, but in such a method, the amount of heat required for the production of isoprene is considered. The problem is that the use efficiency of the heat exchanger is reduced, high-boiling by-products accumulate in the pipeline, and the pipeline becomes clogged, and the temperature near the heat exchanger surface becomes too high, making it more susceptible to acid corrosion. is there.

On the other hand, if the concentration of the high-boiling by-products exceeds 40% by mass, the pipeline connecting the heat exchanger and the reactor and the internal pipeline of the heat exchanger itself are easily clogged, and the operation trouble The heating efficiency of the reaction mixture by the heat exchanger (heating efficiency) is reduced, the circulating reaction mixture is easily concentrated, and the acid with increased concentration causes corrosion of the equipment. And other problems.

The method for controlling the concentration of the high-boiling by-product in the reaction mixture to be within the above range is not particularly limited. For example, a part of the reaction mixture is taken out (hereinafter, the taken out reaction mixture is taken out). Is sometimes referred to as a “removal reaction mixture”), and at least a portion of high-boiling by-products is removed from the removal reaction mixture by an appropriate removal method described below. A kind of feedback control is a simple control method of returning the mixed solution (hereinafter, sometimes referred to as “reaction mixture after removal”) to the reactor again. In the example of FIG. 1, the reaction mixture is withdrawn from the pipes P 3 and / or P 4, the high-boiling by-product is separated and removed in the high-boiling by-product separation tank 4, and the removed reaction mixture is removed. Return to reactor via line P5. The method for separating and removing high-boiling by-products from the reaction mixture in the high-boiling by-product separation tank 4 is not particularly limited.For example, an extraction method using an organic solvent is preferably used. it can.

The frequency of withdrawing a part of the reaction mixture in the reactor may be continuous or intermittent.The amount of withdrawal may be determined in consideration of the amount of by-products accumulated in the reactor, etc. . For example, in a reactor with an internal volume of 120 L, the concentration of high-boiling by-products in the reaction mixture is determined while continuously withdrawing the reaction mixture at 2 L / hour. Is controlled so as to fall within the range of 0.5 to 40% by mass.

The method for measuring the concentration of high-boiling by-products in the reaction mixture is not particularly limited.For example, if a part of the reaction mixture is extracted and cooled, the high-boiling by-products are solidified. And measuring the mass to calculate the concentration of the high-boiling by-product in the reaction mixture.

The concentration of the formaldehyde aqueous solution should be as high as possible from the viewpoint of reducing the amount of heat given to the accompanying water supplied to the reactor as an aqueous solution, that is, the amount of heat required for the production of isoprene. It is good. Usually, the concentration of the aqueous formaldehyde solution is preferably in the range of 20 to 70% by mass, and more preferably in the range of 25 to 60% by mass. However, if the concentration of the aqueous formaldehyde solution is too high, there is a problem that paraformaldehyde is easily precipitated.

C ₄ used in the present invention is 3-methylbutane-1,1,3-diol, 3-methyl-2-buten-1-ol, 3-methyl-1-buten-1-ol, 3-methyl-1-butene-1-ol Includes 3-ol, methyl isopropyl ketone, 2-methylbutanol, methyl-t-butylformal, 4,4-dimethyl-1,3-dioxane, 4-methyl-5,6-dihydro_2H-pyran, etc. You may go out. It may also contain isobutylene and methyl-t-butyl ether which decomposes into t-butyl under the reaction conditions. The acidic aqueous solution used in the present invention is an aqueous solution of an acidic substance such as an inorganic acid, an organic acid, and salts thereof. As the acidic substance, those having low volatility or non-volatility under the reaction conditions are preferable, for example, inorganic acids (phosphoric acid, sulfuric acid, boric acid, etc.), heteropolyacids (caitungstic acid, phosphotungstic acid, etc.), Organic acids (such as P-toluenesulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid, and oxalic acid), and acid salts (such as sodium hydrogen sulfate).

P H of acidic aqueous solution, the kind of the acidic substance, the reaction temperature, the feed rate of C _4, but may differ due to the feed rate of Horumua aldehyde, usually, p HO. 5 to 2. Is preferably in the range of 5 , PH is more preferably in the range of 1-2.

In the production method of the present invention, it is possible to carry out the reaction while simultaneously supplying a low-boiling compound or an inert gas which is inert under the reaction conditions to the reactor, if necessary, in addition to the reaction mixture. is there. As such low-boiling compounds, hydrocarbons are preferable, and particularly those having 1 to 10 carbon atoms, for example, n-propane, n-butane, n-hexane, cyclohexane and the like can be mentioned. Also, as the inert gas, nitrogen and the like are preferable.

The molar ratio of the reactor is supplied c ₄ and formaldehyde (hereinafter referred to as "c ₄ Horumua aldehyde") is preferably at least 3, and more favorable preferable 5 or more. There is no strict upper limit to the molar ratio. However, if the molar ratio is excessively increased, the effect of improving the yield of isoprene is small, and the amount of heat used in the production of isoprene is increased and the economical cost is increased. Disadvantageous. In general, the C ₄ / formaldehyde content is preferably 20 or less, more preferably 12 or less. Incidentally, if c ₄ 7 formaldehyde is less than 3, isoprene yield tends to decrease.

As apparent from the molar ratio of C ₄ and formaldehyde mentioned above, in the present invention, is used in excess of C ₄ relative to formaldehyde. Thus, distillate and have contact to the production method of the present invention, an excess amount of C ₄ was fed into the reactor is generated isoprene, from the reaction system as a while the reaction distillation gas, unreacted with low-boiling components and water However, the unreacted C ₄ distilled out of the reaction system is separated and recovered from other distillate components, Can be reused in manufacturing methods.

The unreacted c ₄ distilled out of the reaction system has a composition close to the equilibrium composition of isobutylene and t-butanol under the reaction conditions. That is, even if only one of isobutylene and t-butanol is supplied as a starting material to the reactor in the production method of the present invention, unreacted raw materials are separated from the viewpoint of reducing the unit consumption of the raw materials. If separated, collected and reused, a mixture of isobutylene and toluene will be used as a raw material.

As described above, in the present invention, C ₄ , formaldehyde and water are supplied continuously or intermittently to an acidic aqueous solution, and from this reaction mixture, the produced isoprene, water, unreacted raw materials and other low-boiling components are removed. The reaction is carried out while distilling the mixture containing it out of the reaction system as a reaction distillate gas.

In order to obtain isoprene at a high yield, the pressure in the reactor (however, when a low-boiling compound that is inactive under the reaction conditions is supplied together with the raw materials, the pressure obtained by subtracting the partial pressure) depends on the reaction temperature. It is preferably in the range of 1.1 to 2.5 times the vapor pressure of the acidic aqueous solution, and more preferably in the range of 1.1 to 2 times.

The vapor pressure of the acidic aqueous solution at the reaction temperature (hereinafter, abbreviated as Pw) is a physical constant uniquely determined by the type and concentration of the acidic substance contained in the reaction mixture. If the pressure in the reactor exceeds 2.5 times Pw, the yield of isoprene tends to decrease significantly. On the other hand, when the pressure in the reactor is less than 1.1 times Pw, the yield of isoprene does not decrease remarkably, but the conversion of formaldehyde decreases and isoprene in the reaction distillate gas. As the ratio of water to water increases, the amount of heat consumed in the reaction, that is, the amount of heat required to produce isoprene, increases, which is economically disadvantageous.

The suitable reaction temperature in the present invention is determined in consideration of the acid concentration in the reaction mixture, and is usually preferably in the range of 150 to 220 ° C. When the reaction temperature is lower than 150 ° C., the yield of isoprene tends to decrease even if the concentration of the acidic aqueous solution is increased to maintain the reaction rate at a constant level. On the other hand, the reaction temperature exceeded 220 ° C Although the selectivity of isoprene does not decrease remarkably, the reaction conditions under which the conversion of formaldehyde under the condition giving the optimum selectivity decreases and the conversion of formaldehyde increases conversely are selected. It is not beneficial because the sequential reaction from isoprene proceeds to increase by-products, and as a result, the selectivity of isoprene decreases.

The preferred supply rate of the formaldehyde source (aqueous formaldehyde solution) to the reactor is determined in consideration of the concentration of the acid in the reaction mixture, the reaction temperature and the reaction pressure. To increase the supply rate of the formaldehyde source, It is necessary to increase the concentration of the acid in the mixture or increase the reaction temperature, in which case the corrosion of the reactor occurs. There is no lower limit on the supply rate of the formaldehyde source, but if it is too small, the volumetric efficiency will deteriorate. Therefore, the supply rate of the formaldehyde source is usually preferably in the range of 0.2 to 3 mol hours in terms of formaldehyde per 1 kg of the reaction mixture, and more preferably in the range of 0.5 to 2 mol / hour. More preferred.

The amount of water supplied to the reactor is usually adjusted so that the amount of the reaction mixture in the reactor is kept constant. That is, the amount is determined by the amount of water distilled from the reactor and the amount of water increased or decreased by the reaction.

As described above, since the boiling point of water is high among the components that make up the reaction distillate gas, if the pressure inside the reactor is high, the proportion of water to the total components other than water in the reaction distillate gas decreases. However, when the pressure is low, the proportion of water increases. Therefore, it can be said that the ratio of the number of moles of water distilled from the reactor to the number of moles of the raw material and product distilled out is determined by the pressure in the reactor. Further, the number of moles of starting material and product distilled, since approximately equal to the number of moles of C ₄ supplied, also the ratio of C ₄ supplied with water being distilled may be defined by the pressure in the reactor. Therefore, the amount of water to be supplied, the pressure in the reactor may be determined in consideration of the increase and decrease of water by supply amount and reactivity of c _4.

As described above, high-boiling by-products are generated and accumulated in the reaction mixture as the reaction is performed for a long time. Since the high-boiling by-products are separated and dispersed in the reaction mixture, a part of the reaction mixture in the reactor is continuously or intermittently withdrawn, and a high-boiling by-product separation tank (for example, , Decanter, extraction tower, etc.) Remove at least some of the by-products and control their concentration.

However, this high-boiling by-product has a small difference in specific gravity with respect to the reaction mixture, and a mixture of large and small specific gravity exists. Therefore, liquid separation operation using a specific gravity difference such as decantation is performed. In addition, since the high-boiling by-product has a property of solidifying at room temperature, the temperature of the reaction mixture is once lowered to solidify the high-boiling by-product and then separated and removed. However, it is necessary to reheat the reaction mixture. From these points, in order to facilitate the separation of the reaction mixture and the high-boiling by-products, it is preferable to extract and remove using an extraction solvent.

Such an extraction solvent is preferably a hydrocarbon having a lower boiling point than water, a low solubility in water, and a liquid at normal pressure, such as n-hexane and cyclohexane.

As an extraction solvent, a compound obtained as a distillation residue obtained by distilling unreacted raw materials and isoprene from an organic substance contained in a reaction distillate gas distilled out of the reactor out of the reaction system, or a compound thereof. Part components can also be used. Compounds contained in the distillation residue include 4-methyl-5,6-dihydro-12H-pyran, methylisopropylketone, 2-methylbutanol, 2,6-dimethyl-2,5-butadiene, 2,6-Dimethyl-1,5-butadiene, 3-methyl-3-buten-2-ol, and the like. In addition, compounds having various functional groups having 4 to 15 carbon atoms are also available. include.

When carrying out the production method of the present invention, a heating device is provided in the reactor itself in order to secure the amount of heat required for producing isoprene and the amount of heat required for distilling isoprene, water, unreacted raw materials and other low-boiling components. Although it may be provided, a mode in which a suitable auxiliary heating device is provided is preferable. For example, as shown in Fig. 1, a heat exchanger 3 is arranged outside the reactor as an auxiliary heating device, and a reaction between the reactor 1 and the heat exchanger 3 is performed through pipes P7 and P9. As an example of a configuration in which the mixture is circulated, an embodiment in which the reaction mixture is heated is exemplified.

In this embodiment, the reaction mixture is circulated as it is to an external heat exchanger and heated. Since the amount of isobutylene dissolved in the reaction mixture is small, the boiling point rises in the reactor, and the temperature of the reaction mixture in the heat exchanger rises significantly. An increase in the temperature of the reaction mixture causes an increase in side reactions, which leads to a decrease in isoprene yield. To prevent this, as shown in FIG. 1, the reaction mixture was extracted in conduit P 7 for circulation, adding at least a portion of the C ₄ through conduit P 8, the heat exchanger together these A preferred embodiment is that the mixture is heated in the vessel 3 and introduced into the reactor 1 through the line P9.

However, compared to isobutylene, t-butyl alcohol prevents the temperature of the reaction mixture from rising due to heating, and is much less effective. Moreover, t - flop evening Nord is by contact with an acidic aqueous solution in the heat exchanger, converted into Isopuchiren, for the first time show the effect described above, as the c ₄ be added to the reaction mixture were removed for circulating heating And isobutylene are preferred.

In the present invention, the calorie of the reaction distillate gas can be recovered and used effectively for the production of isoprene.

As an embodiment of the calorie recovery, for example, there is an embodiment in which mainly the water in the reaction distillate gas is condensed to recover the heat of the water (for example, in FIG. Shrinking.)

As for the use of the recovered heat, the heat of the uncondensed reaction distillate gas is used as a heat source for vaporizing isobutylene (for example, in FIG. 2, the heat source is used in the heat exchangers 6 and 7). In addition, the heat source when unreacted isobutylene in the organic layer obtained by condensing the reaction distillate gas and phase-separating it is recovered by distillation (for example, in Fig. 2, it is used as the heat source in the heat exchanger 11). To generate steam by exchanging the reaction distillate gas with water for heat exchange, and to directly convert the reaction distillate gas into the recovery of isobutylene, the recovery of toluene, or the recovery or purification of isoprene. Introduced into a reboiler of a distillation column used at that time, and used as a heat source of the reboiler. In FIG. 2, the steam obtained by the heat exchanger 5 may be used as the heating steam in the heat exchanger 11 or the like. In the present invention, as described above, a part of the reaction mixture is continuously or intermittently controlled in order to control the concentration of the high-boiling by-product in the reaction mixture within the range of 0.5 to 40% by mass. To a decanter, an extraction column, etc., and remove at least a part of high-boiling by-products from the reaction mixture.

Since the method of removing the high-boiling by-product is the point of the present invention, the present inventors have further studied. As a result, as described above, some of the accumulated high-boiling by-products have a large specific gravity and a small specific gravity with respect to the reaction mixture, and have a specific gravity relative to the reaction mixture in the reactor. It has been found that large high-boiling by-products tend to collect at the bottom of the reaction mixture, that is, at the bottom of the reactor, and high-boiling by-products having a low specific gravity tend to collect at the top of the reaction mixture.

Therefore, in a preferred embodiment of the present invention, at the time of removing high-boiling by-products from the reaction mixture, an outlet for the reaction mixture is provided at least at the bottom of the reactor. For example, in FIG. 1, a sampling line P3 is provided at the center of the bottom of the reactor. By using this withdrawal line P 3, high-boiling by-products having a higher specific gravity than the reaction mixture are removed outside the reactor when a part of the reaction mixture is continuously or intermittently withdrawn. It is easier to do. It is preferable that such a discharge port is provided at the center of the bottom of the reactor, but the present invention is not limited to this.

Similarly, in a preferred embodiment of the present invention, in order to facilitate removal of a high-boiling by-product having a low specific gravity with respect to the reaction mixture, the outlet of the reaction mixture is provided at the side wall of the reactor (reactor). On the side wall of the fuselage). In this case, the height of the withdrawal port is such that the volume of the liquid when the reaction mixture is filled up to that height is at least 1/2 of the total volume of the reaction mixture to be accommodated at the start of production, and more preferably It is preferable that the height is set to be 2/3 or more (hereinafter, abbreviated as height h). By providing a sampling port at this height h, when a part of the reaction mixture is continuously or intermittently extracted, high-boiling by-products having a lower specific gravity than the reaction mixture can be easily obtained. It can be removed. By providing a reaction mixture outlet at both the bottom and side walls of the reactor, high-boiling by-products can be efficiently removed from the reaction mixture in the reactor regardless of the specific gravity of the reaction mixture. And the concentration of the high-boiling by-product can be more easily controlled within the range of 0.5 to 40% by mass.

If no outlet for the reaction mixture was provided at the bottom of the reactor, as the reaction was performed for a long time, high-boiling by-products having a higher specific gravity than the reaction mixture were found at the bottom of the reactor. As it accumulates, it becomes difficult to control the concentration of the high-boiling by-product in the reaction mixture within the range of 0.5 to 40% by mass. Then, there arise problems such as a decrease in the heating efficiency of the reaction mixture and a blockage of the pipeline, and a problem that a steady state of the reaction cannot be maintained due to a change in the concentration of the acid in the reaction mixture or the composition ratio of the raw materials.

If the reaction mixture outlet is not provided on the side wall of the reactor, the reaction proceeds over a long period of time, and the high-boiling point with a lower specific gravity than the reaction mixture is placed above the reaction mixture. As the products accumulate, it becomes difficult to control the concentration of the high-boiling by-product within the range of 0.5 to 40% by mass. Then, distilling out of the reaction mixture of isoprene, water, unreacted raw materials and other low-boiling components out of the reactor as a reaction distillate gas is hindered. This raises the problem that the steady state of the reaction cannot be maintained due to the rise, fluctuations in the concentration of the acid in the reaction mixture and the composition ratio of the raw materials. Furthermore, when the amount of the reaction distillate gas reduced, the amount of aqueous formaldehyde solution supplied to the reactor had to be reduced in order to maintain the level of the reaction mixture in the reactor at a constant level. Production volume decreases.

An example of a preferred configuration of the reaction apparatus for controlling the concentration of the high-boiling by-product in the reaction mixture within the range of 0.5 to 40% by mass will be described with reference to FIG. A stirrer (an external drive is not shown) is provided so that the stirring blade W rotates horizontally in the reaction mixture in the reactor, and a pipe P 6 for supplying C _{4 is connected} to the stirring blade in the reactor. extending to just below the., from inlet P 6- 1 to impinge the C ₄ to stirring blade, supplied preferably is ejected.

If C ₄ hits the stirring blade, the distance between the stirring blade and the supply port of C ₄ must be strict. Although not limited in the sense, from the viewpoint of dispersion efficiency of c _4, for example, when the distance to the heart tip during the rotation of the stirring blade is 2 m, usually 0. Is preferably a range within 3 m , 0.2 m or less. When C ₄ is supplied without hitting the stirring blade, the gas and liquid in the reaction mixture in the reactor are not sufficiently dispersed, and the amount of high-boiling by-products is increased. The concentration of high-boiling by-products accumulated in the reaction mixture tends to increase.

There is no particular restriction on the inlet P 6- 1 in the form of C _4, an inlet port P 6- 1 is curved tubes that make up the ring, supplied at appropriate intervals on its circumference An embodiment in which a mouth is provided is preferred. In this case, it is preferable that the radius of curvature of the ring-shaped inlet P6-1 is 50 to 80% of the distance from the rotation center of the stirring blade to the tip. The interval between the supply ports provided on the circumference of the ring-shaped inlet port P6-1 is preferably such that the circumference is equally divided by 5 to 100, and is equally divided by 10 to 40. A degree interval is more preferred.

As described above, when circulating the reaction mixture between the reactor and the external heat exchanger, and a C ₄ was added to the reaction mixture was heated by an external heat exchanger, it is preferably returned to the reactor again (Pipes P7, P8 P9 in Fig. 1) o

As a preferred embodiment when returning the reaction mixture to the reactor, for example, as shown in FIG. 1, the reaction mixture heated after the addition of C ₄ and then in the heat exchanger 3 is transferred to a pipe P 9. To the lower part of the reactor, and supply it so as to hit the stirring blade W. This makes it possible to sufficiently disperse the gas and the liquid in the reaction mixture in the reactor, to suppress an increase in the concentration of the high-boiling by-product, and to easily control the concentration. Here, the lower part of the reactor is not particularly limited as long as the reaction mixture strikes the stirring blade when the reaction mixture is introduced again into the reactor, but the reaction mixture is introduced into the reactor from below the stirring blade. Is preferred.

If the reaction mixture returned from the heat exchanger to the reactor is not supplied so as to hit the stirring blade via line P9, the gas and liquid in the reaction mixture in the reactor become insufficiently dispersed. The amount of high-boiling by-products increases and accumulates in the reactor, The concentration in the reaction mixture tends to increase.

In the present invention, as the water to be supplied to the reactor, water may be decomposed from the reaction distillate gas, and the water thus decomposed may be reused (hereinafter, dewatered from the reaction distillate gas and reused). The water used is abbreviated as “recycled water.”) For example, in FIG. 2, the water condensed in the heat exchanger 5 is introduced into the distilling receiving layer 8, supplied to the reactor via the pipe P10-1 and the like, and reused.

By supplying such recycled water directly to the reactor, the amount of the reaction mixture in the reactor can be kept constant, and the concentration of the high-boiling by-product in the reaction mixture is 0.5 to 0% by mass. Control within the range becomes easy. In addition, since the temperature of the recycled water is within a range of 120 to 140 ° C (under a pressure of about 1.5 MPa), the amount of heat required for producing isoprene can be reduced. If recycled water is not used, i.e. fresh water (typically about 25 ° C) can still control the concentration of high-boiling by-products in the reaction mixture, but until heated to the reaction temperature This is economically disadvantageous because the amount of heat required increases.

Isoprene can be obtained by fractionating the organic layer of the distillate distilled out of the reaction system by performing the present reaction method. For the steps required until the isoprene is finally fractionated from the distillate distilled from the line P2 in FIG. 1, refer to the known art (for example, Japanese Patent Application Laid-Open No. Sho 60-41838). You may.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

In the following examples, equipment for carrying out the method for producing isoprene of the present invention was actually constructed, and the concentration of high-boiling by-products in the reaction mixture was within the range of 0.5 to 40% by mass. The reaction was continued for 8 hours while maintaining the concentration at various concentrations in each step, and the conversion of formaldehyde, isoprene selectivity and yield in the last hour were controlled for each. Was examined.

In the comparative example, the concentration of the high-boiling by-product in the reaction mixture in the reactor was out of the above range. The significance was confirmed.

(Equipment configuration)

First, an example of a facility constructed for carrying out the method for producing isoprene of the present invention will be described with reference to FIG.

As the reactor 1 was prepared tank having an inner volume of 1 2 0 L, this, C ₄ inlet conduit P 6, an aqueous formaldehyde solution inlet pipe P 1-1, the water inlet pipe P 1-2, an acidic aqueous solution (phosphate (Aqueous acid solution) Inlet line P1_3, distillate line P2 for products, etc., and reaction mixture withdrawal lines P3 and P4 are connected. In addition, the reactor is equipped with auxiliary equipment necessary for reaction control, such as a thermometer, a pressure gauge, a stirrer, and a baffle plate.

To the reactor 1, a 46% by mass aqueous formaldehyde solution, a 2.5% aqueous phosphoric acid solution as an acidic aqueous solution, and water having a molar concentration of 12 times that of formaldehyde were supplied. On the other hand, the C ₄ to 8 times the moles of formaldehyde by preheated evaporated in the heat exchanger 2, supplied to the by ejected reactor to blow the stirring blade from the ring-shaped supply port.

Moreover, the reaction from a mixture extraction pipe P 3 branches the conduit P 7, the sampling One reaction mixture from the reactor is mixed with C _4, heating such mixture through the heat exchanger 3, the reactor To return to When returning the reaction mixture heated in the heat exchanger 3 to the inside of the reactor 1, the reaction mixture was jetted toward the stirring blade so as to hit the stirring blade.

Isoprene generated in the reactor 1 is distilled out of the reactor as a reaction distillate gas through the pipe P2 together with unreacted C ₄ , water, formaldehyde and the like. These reaction distillate gases are sent to the heat exchanger 5. In the heat exchanger 5, heat exchange is performed between the reaction distillate gas flowing into the heat exchange pipe and the cooling water flowing into the heat exchanger (that is, the reaction distillate gas is cooled), and the reaction is performed. Water in the distillate gas is fragmented. In addition, the cooling water that has flowed into the heat exchanger 5 obtains heat from the reaction distillate gas to become steam, and the heat is recovered.

The water decomposed in the heat exchanger 5 is sent to the distilling tank 8.

Part of the water in the distilling tank 8 is supplied directly to the reactor through line P 10-1 to be used for adjusting the amount of the reaction mixture in the reactor, and is also connected to line P 10-2. Heat exchange through Is supplied to the vessel 2, it is used to adjust the molar ratio between formaldehyde and C _4, are fed to the reactor 1 by evaporation with C _4. The remainder of the water in distilling tank 8 is sent to distilling tank 9.

On the other hand, the compounds not condensed in the heat exchanger 5 are condensed in the heat exchangers 6 and 7 and sent to the distillation receiving tank 9, where they are separated into an organic layer and an aqueous layer. The organic layer is sent to the heat exchanger 7 where it is heated, and then sent to the distillation column 10 for separating isobutylene.

The fraction in the distillation column 10 is mainly composed of isobutylene, and is condensed in the heat exchanger 12 and then sent to the distillation receiving tank 13.

After a portion of the fraction containing isobutylene as the main component is heated and evaporated in the heat exchanger 6, a portion is transferred to the heat exchanger 2 to adjust the molar ratio to formaldehyde, and then to the heat exchanger 2. The part is sent to heat exchanger 3 to prevent the boiling point of heat exchanger 3 from rising, and then returned to reactor 1. The remainder of the fraction is returned to the distillation column 10 or separately passed through a step of purifying isobutylene, and then reused as a raw material in the production method of the present invention.

The bottom liquid of the distillation column 10 is mainly composed of isoprene and unreacted t-butanol. By purifying the bottom liquid in the distillation column 14, isoprene is obtained from the top of the column.

On the other hand, the main component of the bottom liquid of the distillation column 14 is t-butanol, which is separately purified and reused in the production method of the present invention. The product is sent to the separation tank 4 and used as an extraction solvent when separating high-boiling by-products from the reaction mixture extracted from the reactor.

The reaction mixture (including high-boiling by-products) in the reactor 1 is withdrawn from each of the outlets provided near the center of the bottom surface of the reactor and on the side of the reaction mixture on the side wall of the reactor. After being mixed with water, the mixture is sent to a high-boiling by-product separation tank 4, where it is separated into an organic layer (extracting solvent) containing a high-boiling by-product and an aqueous layer.

The organic layer is effectively used for applications such as fuel, and the aqueous phosphoric acid solution in the aqueous layer is at least partially recycled to the reactor. Sampling of the reaction mixture for measuring the concentration of high-boiling by-products in the reaction mixture in the reactor can be performed, for example, by providing outlets in the pipelines P3, P4, and P7. While confirming the concentration of the high-boiling by-product in the reaction mixture, stopping and executing the removal of the reaction mixture from the outlet so that the concentration falls within the range of 0.5 to 40% by mass. Is appropriately performed.

Examples 1 to 8

The reaction conditions in the reactor were a reaction temperature of 175 to 178 ° C, a reaction pressure of 1.52 MPa, and a rotation speed of the stirring blade of 48 to 55 rpm.

A reactor (internal volume 120L) was charged with 60L of 2.5% phosphoric acid aqueous solution, and under the above reaction conditions, 46% by mass aqueous formaldehyde solution was 3.24 kg / hour, isobutylene was 17.7 kg / hour, The reaction was started by continuously supplying t-butanol at a rate of 6.02 kg / hour and water at a rate of 9.08 kg / hour.

Twenty-four hours after the start of the reaction, the reaction equipment shown in Fig. 2 [One outlet for the reaction mixture was placed at the center of the bottom of the reactor, and one side (a height of 4/5 of the total volume of the reaction mixture in the reactor) one provided is), when the inlet P 6- 1 to C ₄ was injected to strike the stirring blade from either Tsu via line P 9 reaction mixture back into the reactor, so that hits the stirring blade Fire. Then, a configuration is adopted in which recycled water is again introduced into the reactor from the distilling tank 8. In this case, the concentration of the high-boiling by-products in the reaction mixture is adjusted to a predetermined value as described below by adjusting the removal amount of the high-boiling by-products mainly in the high-boiling by-product separation tank 4. It controlled so that it might become.

The controlled high-boiling by-product concentrations are as follows:

0.5% by mass (Example 1), 1% by mass (Example 2), 2% by mass (Example 3), 5% by mass (Example 4), 10% by mass (Example 5), 20% by mass (Example 6), 30% by mass (Example 7), 40% by mass (Example 8).

Each concentration was kept stable and the reaction was continued for 8 hours, and the conversion of formaldehyde, isoprene selectivity and yield for the last hour were examined. The results are shown in Table 1. Comparative Example 1 4

The concentrations of the high boiling by-products in the reaction mixture were reduced to 0% by mass (Comparative Example 1), 0.3% by mass (Comparative Example 2), 50% by mass (Comparative Example 3), and 60% by mass (Comparative Example). The reaction was carried out in the same manner as in Example 18 except that 4) was maintained, and the conversion of formaldehyde, isoprene selectivity and yield in the last hour were examined. Table 1 shows the results.

table 1

The respective reactions were carried out according to Example 18 and Comparative Example 14. As is clear from Table 1, the concentration of the high-boiling by-product in the reaction mixture was 0.540% by mass (Example 1). By keeping within 8), the steady state of the reaction in the reactor can be maintained, the conversion of formaldehyde is always 98% or more, and the yield of isoprene is always 71% or more. I understand.

From these results, the concentration of high-boiling by-products in the reaction mixture was 0.540 It was found that by maintaining the amount within the range of%, isoprene can be efficiently produced while maintaining the steady state of the reaction.

On the other hand, in Comparative Examples 1 to 4 in which the concentration of high-boiling by-products in the reaction mixture was outside the above range, the conversion of formaldehyde was less than 97%, and the yield of isoprene was always less than 70%. It turned out that.

In Comparative Examples 1 and 2 in which the concentration of the high-boiling by-product in the reaction mixture was less than 0.5% by mass, the efficiency of heating the reaction mixture by the heat exchanger 3 was reduced. As the temperature of the reaction mixture decreased, the conversion of formaldehyde decreased and the yield decreased.

In Comparative Examples 3 and 4, in which the concentration of the high-boiling by-product was set to a value exceeding 40% by mass, the high-boiling by-product accumulated in the pipe connecting the reactor 1 and the heat exchanger 3, It became difficult to send the reaction mixture to the heat exchanger 3, and the heating efficiency in the heat exchanger 3 was reduced. As a result, the conversion rate of formaldehyde and the selectivity for isoprene were reduced due to a decrease in the temperature of the reaction mixture in the reactor, and the yield was reduced.

The method for producing isoprene of the present invention can be carried out by a known method for producing isoprene (for example, see JP-A-56-79628 and HYDROCARBON PROCESSING, page 167 (January 1971). This is advantageous because the manufacturing process is simpler and the utility can be kept low. The fact that the yield improvement which could not be achieved by this method could be increased by about 2% in the present method is extremely advantageous in the field of the present invention from the viewpoint of production cost. .

Industrial applicability

The isoprene obtained by the production method of the present invention is effectively used as a basic chemical raw material for various chemical products and polymer raw materials.

Claims

The scope of the claims

1. Isobutylene and / or t-butanol, formaldehyde and water are continuously or intermittently fed into the acidic aqueous solution, and from this reaction mixture, • isoprene, water, unreacted raw materials and other low boiling points are formed. A process for producing isoprene by distilling a mixture containing components out of the reaction system and reacting the mixture,

2. A reactor containing the reaction mixture is provided with an outlet for the reaction mixture, a part of the reaction mixture is withdrawn from the outlet, and at least one high-boiling by-product is removed from the reaction mixture. 2. The method for producing isoprene according to claim 1, wherein the concentration of the high-boiling by-product in the reaction mixture is controlled within the above range by separating and removing the part, and then introducing the part into the reactor again. .

3. The method for producing isoprene according to claim 2, wherein an outlet for the reaction mixture is provided at least at the bottom of the reactor. '

4. An outlet for the reaction mixture is provided on the side wall of the reactor, and the height of the outlet is adjusted to the height when the volume of the solution is filled with the reaction mixture to the height. The method for producing isoprene according to claim 2 or 3, wherein the height is set so as to be 1/2 or more of the product.

5. A mixture containing the produced isoprene, water, unreacted raw materials and other low-boiling components is distilled out of the reaction system as a reaction distillate gas, and water is condensed from the reaction distillate gas. The production of isoprene according to any one of claims 1 to 4, wherein the concentration of the high-boiling by-product in the reaction mixture is controlled within the above range by introducing water into the reactor again. Method.

6. The reactor is equipped with a stirring device that is configured so that the stirring blades rotate horizontally in the reaction mixture, and the isobutylene and / or t-butyl alcohol is piped to the pipe just below the stirring blades in the reactor. By supplying from the extended inlet to the stirring blade The method for producing isoprene according to any one of claims 1 to 5, wherein the concentration of the high-boiling by-product in the reaction mixture is controlled within the above range.

7. The reactor is equipped with a stirring device that is configured so that the stirring blades rotate horizontally in the reaction mixture, and a part of the reaction mixture is withdrawn from the reactor, and is removed with isobutylene and / or t-butyl. The reaction mixture is heated in a heat exchanger together with at least a part of the evening oil, and then introduced into the reactor again.The heated reaction mixture is supplied to the stirring blade through an inlet provided in the reactor. 7. The method for producing isoprene according to claim 1, wherein the concentration of the high-boiling by-product in the mixture is controlled within the above range.